1. Field of the Invention
The present invention relates to a pressure damper of an ink jet printer, and provided between an ink jet head and an ink feed source to absorb a pressure fluctuation of an ink to be fed to the ink jet head.
2. Description of the Related Art
FIG. 12 shows a known typical ink jet printer in which an ink tank (cartridge) 2, which contains a vacuum-degassed liquid ink, is connected by an ink feed tube 8 to an ink jet head 4 carried by a head carriage 6. The ink jet head 4 has jet nozzles 4b (FIG. 13) from which an ejection of ink onto a recording medium (paper etc.) 10 is controlled by a control unit (not shown). The head carriage 6, which supports the ink jet head 4, is moved by the control unit along guide bars 7a and 7b in the opposite directions shown by an arrow, and upon printing, the jet nozzles 4b are moved closer to a platen 12. The ink jet head 4 is provided therein with pressure chambers 4c (FIG. 13) corresponding to the nozzles 4b, and piezoelectric elements 4d (FIG. 13) opposed to the pressure chambers 4c, so that the volume of the pressure chambers 4c can be reduced by the associated piezoelectric elements 4d at a predetermined time sequence and in a predetermined pattern, to eject the ink from the associated jet nozzles connected to the pressure chambers 4c to thereby perform the printing on the recording paper 10, which is than moved upward by the platen 12.
In the kind of serial type ink jet printer mentioned above, during the reciprocal movement (forward movement and return movement) of the ink jet head 4, an acceleration force is applied to the ink jet head or to the ink itself in the ink passages in the ink jet head, and a pressure change occurs in the ink due to the inertia thereof, thus resulting in a failure to provide a stable ejection of ink from the jet nozzles 4b. Namely, when the pressure in the pressure chambers 4c is reduced by the associated piezoelectric elements 4d, the increased pressure due to the pressure reduction of the pressure chambers is absorbed by air bubbles, and thus the increased pressure can not be effectively transmitted to the ink, and accordingly, an ejection of ink from the jet nozzles cannot be obtained.
To reduce the effect of the pressure change, a pressure damper is usually provided in the ink feed line.
Furthermore, for example, upon an exchange of the ink tank (cartridge), foreign matter, such as fine particles or air bubbles, may enter the ink feed line, resulting in a blocking or plugging of the jet nozzles, and this is prevented by a mesh filter provided in the ink feed line.
When an irregular ejection of ink occurs in the ink jet head, purging is carried out to pressurize or exert a suction force on the ink in the ink line, to thereby force the foreign matter out of the plugged nozzles.
FIG. 13, 14, and 15 show a known pressure damper 16 usually provided in the ink feed tube 8 between the ink tank 2 and the ink jet head 4, as shown in FIG. 12.
As can be seen in FIGS. 14 and 15, the pressure damper 16 has a plate-like main body 20 made of polyethylene and provided with holes and channels on the opposite side faces thereof which are closed by flexible films 22 and 24 secured to the opposite side faces of the main body 20, so that the channels define an ink passage and the holes define a pressure absorber. Namely, the side faces 20a and 20b of the main body 20 are provided at the central portions thereof with pressure absorbing portions 26a and 26b (pressure absorbing chamber 26) which are defined by circular recesses interconnected by a connecting hole 28. An ink inlet plug portion 27 to which the ink feed tube is inserted is formed in the vicinity of the upper end of the main body 20. The ink inlet passage 22, which is defined by the channel formed in the main body 20, is formed in one side 20a of the main body 20 to be connected to an inlet port 25 of the inlet plug portion 27. The ink inlet passage 22 is also connected to the first pressure absorbing portion 26a.
Similarly, an ink outlet plug portion 31 is formed on the opposite side of the main body 20 to the ink inlet plug portion 27, in which the ink feed tube 8 is inserted. An ink outlet port 33 of the ink outlet plug portion 31 is connected to an ink outlet passage 35, which is defined by the channel formed in the main body 50, and the ink outlet passage 35 is connected to the first pressure absorbing portion 26a.
The pressure fluctuation of the ink is absorbed by elastic deformations (vibration) of the flexible films 22 and 24 on the opposite sides of the main body 20. The ink feed tube 8a (FIG. 13) between the ink tank 2 and the pressure damper 16 is connected at one end thereof to an ink feed port 2a of the ink tank 2. The ink feed tube 8b between the pressure damper 16 and the ink jet head 4 is connected at one end thereof to a common ink chamber 4a of the ink jet head 4 and at the opposite end to the ink outlet port 33 of the ink outlet plug portion 31 of the pressure damper 16.
The mesh filter 17 is provided upstream of the pressure damper 16, to trap foreign matter such as relatively large air bubbles or fine particles.
As can be understood from the foregoing, in the prior art shown in FIGS. 13 to 15, the pressure fluctuation of the ink is absorbed by the pressure damper 16 and the foreign matter is caught by the mesh filter 17, so that almost no foreign matter enters the pressure damper 16. The pressure damper 16, however, is a separate unit from the mesh filter 17, thus resulting in an increased size of the apparatus. Furthermore, fine air bubbles not trapped by the mesh filter 17 enter the pressure damper 16 and collect in the upper portion of the pressure absorbing portions 26a and 26b, as shown at 18 in FIG. 13. To eliminate these air bubbles 18, the above purging is carried out. The purge device 23, which includes a purge pump 29 and a purge sucker 30 connected thereto as shown in FIG. 13, is usually provided outside the printing area. When the purging is effected, the ink jet head 4 is automatically moved in front of the purge device 23 by a drive (not shown), so that the nozzles 4b are opposed to the purge sucker 30. The subject of the present invention is not directed to the purge, which is per se known, and accordingly, a detailed description thereof is not given herein.
During the purge, the air bubbles 18 in the pressure damper 16 are sucked through the ink outlet passage 35 of the pressure damper 16, but the relatively large bubbles trapped by the mesh filter 17 can not pass through the mesh filter 17, because of an interfacial force of the ink, and thus the bubbles together with the fine particles remain trapped by the mesh filter 17. Accordingly, the effective filtering opening area is often reduced after a long time use thereof. To prevent this reduction of the area, it is necessary to use a large size of mesh filter, resulting in an increased size of the apparatus.